Transceivers are widely used in many modern wireless communication devices (e.g., cell phones, wireless sensors, PDAs, etc.). Transceivers are able to transmit and receive electromagnetic radiation using an antenna. Some transceivers are able to operate as full duplex systems, which transmit and receive data at a same time.
FIG. 1 illustrates a transceiver 100 that can operate as a full duplex system. The transceiver 100 comprises a transmission path 102 and a reception path 108. The transmission path 102 comprises a power amplifier 110 that is configured to provide a signal having a first frequency S(f1) within a transmission band-width to an antenna 106. The reception path 108 comprises a low noise amplifier 112 that is configured to receive a received signal having a second frequency S(f2) within a reception band-width from the antenna 106. A duplex filter 104 is located between the transmission and reception paths, 102 and 108, and the antenna 106. The duplex filter 104 is configured to isolate the transmission path 102 from the reception path 108.
The duplex filter 104 comprises a first bandpass filter 104a and a second bandpass filter 104b. The first bandpass filter 104a attenuates noise outside the transmission band-width (e.g., thermal noise input to power amplifier 110 in the transmission path and noise from the power amplifier) from the transmission path 102 before it gets to antenna 106. The second bandpass filter 104b suppresses signals outside the reception band-width including the transmitted signal S(f1) before it gets to the reception path 108. Without the duplex filter 104 the noise and signal from the transmission path 102 may leak into reception path 108, reducing the signal-to-noise ratio and increasing the dynamic range requirements for the receiver.